"Six Degrees of Kevin Bacon is a trivia game based on the concept of the small world phenomenon and rests on the assumption that any actor can be linked through his or her film roles to actor Kevin Bacon within six steps.

The game requires a group of players to try to connect any film actor in history to Kevin Bacon as quickly as possible and in as few links as possible. In 2007, Bacon started a charitable organization named SixDegrees.org. The fantasy author-editor Richard Gilliam devised his Movie Links online game in 1990, and it was played extensively on GEnie four years before the quite similar Six Degrees of Kevin Bacon game was promoted in 1994. Gilliam's game was much more difficult in that a player was required to find the shortest number of movies linking actors as diverse as, say, Gloria Swanson and Chris Farley, rather than continual links to the same specific actor.

History
Kevin Bacon, in a 1994 Premiere magazine interview for the film The River Wild, while talking about his fame and career, commented that he had worked with everybody in Hollywood or someone who's worked with them.

Six Degrees of Kevin Bacon first surfaced at about the same time. On April 7 1994, a lengthy newsgroup thread headed "Kevin Bacon is the Center of the Universe" appeared.

The game was created in early 1994 by three students at Albright College, Craig Fass , Brian Turtle and Mike Ginelli. According to an interview with the three in the Spring 1999 issue of the college's magazine, The Albright Reporter, they were watching Footloose during a heavy snowstorm. When the film was followed by Quicksilver, they began to speculate on how many movies Bacon had been in and the number of people he had worked with.

In the interview, Brian Turtle said, "It became one of our stupid party tricks, I guess. People would throw names at us, and we'd connect them to Kevin Bacon."

The trio wrote talk show host Jon Stewart a letter telling him that "Kevin Bacon was the center of the entertainment universe" and explaining the game. They appeared on The Jon Stewart Show and The Howard Stern Show with Bacon to explain the game. Bacon admitted that he initially disliked the game because he believed it was ridiculing him, but he eventually came to enjoy it. The three inventors released a book, Six Degrees of Kevin Bacon, with an introduction written by Bacon. A board game based on the concept was released by Endless Games.

By the 2000s, the game was familiar enough to be referred to in American popular culture. For example, in an episode of NBC's Will & Grace titled "Bacon and Eggs", Bacon makes a guest appearance, playing himself. During this episode, he makes an obvious reference to the game when talking with Will (played by Eric McCormack):

Will: You — you did a movie with Val Kilmer?
Kevin: No, but Val was in Top Gun with Tom Cruise, and Tom was in A Few Good Men with me. Huh, that was a short one.

Bacon also appeared in a commercial for the Visa check card that parodied the game. In the commercial, Bacon wants to write a cheque to buy a book, but the clerk asks for his ID, which he does not have. He leaves and returns with a group of people, then says to the clerk, "Okay, I was in a movie with an extra, Eunice, whose hairdresser, Wayne, attended Sunday school with Father O'Neill, who plays racquetball with Dr. Sanjay, who recently removed the appendix of Kim, who dumped you sophomore year. So you see, we're practically brothers."

The concept was also presented in an episode of the TV show Mad About You dated November 19, 1996 in which a character expressed the opinion that every actor is only three degrees of separation from Kevin Bacon. Bacon spoofed the concept himself in a cameo he performed for the independent film, We Married Margo.

Bacon provides the voice-over commentary for the NY Skyride attraction in the Empire State Building in New York City. At several points throughout the commentary, Bacon alludes to his connections to Hollywood stars via other actors with whom he has worked.

Bacon numbers

The Bacon number of an actor or actress is the number of degrees of separation he or she has from Bacon, as defined by the game. This is an application of the Erdős number concept to the movie industry. The higher the Bacon number, the farther away from Kevin Bacon the actor is.

The computation of a Bacon number for actor X is a "shortest path" algorithm:

If the lowest Bacon number of any actor with whom X has appeared in a movie is N, X's Bacon number is N + 1.
Kevin Bacon himself has a Bacon number of 0.
Here is an example, using Elvis Presley:

Elvis Presley was in Change of Habit (1969) with Edward Asner
Edward Asner was in JFK (1991) with Kevin Bacon
Therefore Asner has a Bacon number of 1, and Presley (who never appeared in a film with Bacon himself) has a Bacon number of 2.

As of December 2007, the highest finite Bacon number reported by the Oracle of Bacon is 8. The American Civil War general William Rufus Shafter is frequently cited as having a Bacon number of 10, but his number is in fact only 7. If only feature films (and not documentaries) are included, however, he cannot be linked to Bacon at all.

Undefined Bacon numbers
A few actors have an undefined Bacon number, meaning that they cannot be linked to Bacon in any number of connections at all. According to the Oracle of Bacon website, approximately 12% of all actors cannot be linked to Bacon using its criteria.

The center of the Hollywood universe, aka The Hub of Hollywood
While at the University of Virginia, Brett Tjaden created the Oracle of Bacon, a computer program that uses information on some 800,000 people from the Internet Movie Database (IMDb). The algorithm calculates "how good a center" an individual IMDb personality is, i.e. a weighted average of the degree of separation of all the people that link to that particular person. The site returns an average personality number, i.e. for Clint Eastwood, it returns an average "Clint Eastwood Number." From there the Oracle site posits "The Center of the Hollywood Universe" as being the person with the lowest average personality number. Kevin Bacon, as it turns out, is not the "Center of the Hollywood Universe" (i.e. the most linkable actor). In fact, Bacon does not even make the top 1000 list of average personality numbers. Since average personality numbers are dynamic (mercurial) and can change with each new film made, the Center can and does shift. "Centers" have included Rod Steiger, Donald Sutherland and Dennis Hopper (the current Center). Karen Black is the current and all time highest woman in the list."